The present invention concerns the preparation of a sample for the microbiological analysis of a liquid.
It is known that there are liquids which may contain different types of microorganisms, among which the microbiological analysis must only concern one or several types.
These liquids exist for example at the end of a manufacturing chain for monoclonal antibodies. More particularly, such liquids, bearing eukaryotes which have enabled the antibodies to be produced, may possibly be contaminated with bacteria and/or viruses.
The presence of the eukaryote cells may hinder the microbiological analysis of the bacteria and viruses either by liberating toxins which may adversely affect the growth of the microorganisms in the case of conventional detection on a gel growth medium (detection of false negatives) or by perturbing the reading of the results in the case of fast detection (detection of false positives) by luminescence, fluorescence, by amplification or hybridization or by any other method of analysis of the nucleic acids of those microorganisms.
In order to carry out a reliable analysis of this type of liquid, it is thus appropriate to prepare a sample in which selection has been made of only the microorganisms (the bacteria and/or viruses in the example given above) belonging to the types of microorganisms which it is desired to detect.
Methods are already known for preparing a sample for the analysis of a liquid in which the microorganisms to detect are selected by exploiting the differences in morphological characteristics (physical and/or chemical) between the different types of microorganisms.
More particularly, a method of preparation is already known comprising a step of selection consisting of adding into the liquid to analyze a reagent adapted to carry out a specific lysis of the microorganisms belonging to the types of microorganisms which it is not desired to keep in the sample, then of filtering the liquid on a membrane so as to collect on that membrane a sample containing solely the microorganisms to detect and which have not reacted specifically with the lysing agent (those having undergone the lysis being destroyed and having passed through the membrane). The sample so collected is then retrieved to be analyzed with conventional or fast microbiological analysis techniques.
Another solution also for forming the sample consists of separating the microorganisms to keep from the others by virtue of their differences in mass by centrifuging at low speed.